This invention relates to heat-curable silicone rubber compositions. More particularly, this invention relates to a heat-curable silicone rubber composition whose cure yields silicone rubber that has a high mechanical strength and excellent electrical insulating properties and in particular excellent high-voltage electrical insulating properties.
Room temperature-curing silicone rubber compositions that contain zinc carbonate powder are already known (Japanese Patent Publication (Kokoku)Number Sho 53-15939 (15,939/1978)). These silicone rubber compositions cure to yield highly flame-retarded silicone rubbers. However, the cure of this type of silicone rubber composition develops gradually at room temperature in the presence of moisture through a condensation reaction, and several days are required for such compositions to cure completely. Moreover, the cured product has a low mechanical strength and cannot be used in some applications.
As a result of extensive investigations directed to solving the problems described above, the inventors discovered that the admixture of large amounts of zinc carbonate powder or basic zinc carbonate powder into a particular heat-curable silicone rubber composition provides silicone rubber with a high mechanical strength and excellent electric properties and in particular excellent high-voltage electrical insulating properties. The present invention was achieved as a result of this discovery.
Specifically, the object of the present invention is to provide a heat-curable silicone rubber composition that is cured by heating and thereby provides silicone rubber with a high mechanical strength and excellent electrical properties and in particular excellent high-voltage electrical insulating properties.